Sensor activated weft tension device

ABSTRACT

According to a method and apparatus for controlling the insertion process of a weft yarn, the weft yarn is temporarily exposed to a braking friction and the yarn tension is mechanically picked-up. In order to prevent the friction from having a disturbing or damaging effect on the yarn, the yarn tension is only temporarily picked-up during certain phases of the insertion process, in order to derive information from the tension curve that is useful for the control of the insertion process. In a power loom, in particular a jet, rapier or gripper shuttle loom, a tension sensor for sensing the tension of the weft yarn can be switched during insertion between its sensing position and a passive position in which it does not touch the weft yarn. Preferably, the tension sensor is integrated in the insertion brake or even forms the braking element itself.

FIELD OF THE INVENTION

The present invention refers to a method of the type wherein theinsertion process for a weft yarn into a loom includes exposing the weftyarn to a braking friction and detecting the yarn tension of the weftyarn, and further relates to a loom of the type which includes a weftyarn feeder, a weft yarn insertion brake and a tension sensor fordetecting the weft yarn tension.

DESCRIPTION OF THE INVENTION

In the case of a loom known from EP-A2-0 357 975, a tension sensor andan insertion brake are provided downstream of the weft yarn feeder, theinsertion brake being controlled in response to the weft yarn tensionbehavior detected by the tension sensor. However, the tension sensorapplies, just as the insertion brake, friction to the weft yarn duringthe insertion process, and, taking into account the high insertionspeeds and short insertion times which are nowadays used, this frictionapplied is disadvantageous, because a frictional load on the weft yarnalso during critical acceleration and high-speed phases exerts anundesirable influence on the development of the insertion process andmay damage and possibly break the weft yarn. During the control of theinsertion process, the permanently active tension sensor will apply africtional load to the weft yarn in an undesirable manner even at timesat which said weft yarn should be transported as unhindered as possible.

EP-A1-03 56 380 and EP-A1-01 55 431 disclose controlled weft yarninsertion brakes for jet looms, which, in correspondence with thesequence of motions of the weft yarn during the insertion process,become effective in a controlled manner only at intervals for dampingthe increase in tension which will inevitably occur towards the end ofthe insertion process due to a whipping effect. In connection with theseair-jet looms, it is known to decelerate the weft yarn at the end of theinsertion process when a high tension peak occurs due to a whippingeffect in the weft yarn resulting from the fact that the weft yarn isstopped; this tension peak may break, locally elongate or retract theweft yarn and it may cause said weft yarn to assume a wavy shape. Thebraking operation should start a short time before the tension peakoccurs, but its intensity and duration should only be of such a naturethat the tension peak is reduced, that the weft yarn is in the maximumpossible stretched condition before the period of time predetermined forthe insertion process expires, and that the free end of the weft yarnreaches the end of the shed before the reed beats up. Hence, the controlof the braking operation should precisely be adapted to the actualsequence of movements of the weft yarn during the insertion process.Information on the weft yarn movement which can be used for controllingthe braking operation are, for example, passage signals which areproduced in the weft yarn feeder when the yarn is drawn off. The momentat which the tension peak occurs is an additional, useful and preciseinformation for the termination of the insertion process and forcontrolling the braking operation for subsequent insertion processes; onthe basis of said information, a possibly existing difference betweenthe movement of the weft yarn coming from the weft yarn feeder and thedeviating movement of the weft yarn end in the shed--which deviationmay, for example, be caused by a take-off balloon--can be taken intoaccount for controlling the braking operation at the right moments.Furthermore, due to the increase in tension occurring when the reedbeats up, the measure of detecting the tension additionally suppliesinformation which will show whether the insertion process has properlybeen terminated before the beat up takes place, and, prior to this, saidmeasure of detecting the tension also supplies information which willindicate the fact that the insertion process has been started properlyas well as the moment at which the weft yarn is released by the yarnfeeder for drawing off, said last-mentioned information being suppliedon the basis of a tension drop which is detected when the yarn startsits movement at the beginning of the insertion process. If deviations ofthe tension behavior or temporal deviations of predetermined tensionvariations which are to be expected occur, it will be possible to makefailure reports, to switch off the device, if necessary, or to makecorrections for future insertion processes for gradually obtaininginsertion processes which have been optimized to a large extent. Thedetection of the tension, which is carried out by a permanently activetension sensor and which is extremely useful for the above-mentionedpurposes because it is simple and because it supplies the necessaryinformation, is, however, disadvantageous insofar as it will interferewith the insertion process in phases which are extremely critical as faras a frictional influence on the weft yarn is concerned.

In rapier looms, the weft yarn should be decelerated at the beginning ofthe insertion process for guaranteeing that the weft yarn end is takenup reliably, in the intermediate phase, when the weft yarn end is takenover, it should be decelerated for guaranteeing a reliable take over,and at the end of the insertion process it should be declerated forguaranteeing that the weft yarn is correctly stretched and reliablyreleased. Up to now, braking has, for example, been effectedcontinuously, but this causes high increases in tension when the weftyarn is accelerated after having been taken up and taken over. A tensionsensor which, separately from the insertion brake, permanently detectsthe tension mechanically will, however, apply frictional forces to theweft yarn in the acceleration phases, said frictional forces resultingin malfunctions and overlapping the effect of the insertion brake in anundesirable manner.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a method of thetype mentioned at the beginning as well as a loom and an insertion brakeby means of which the weft yarn insertion processes can be optimizedwith respect to the insertion time which is predetermined by the type ofloom used and with respect to a careful treatment of the weft yarn.

In the case of said method, this object is achieved by detecting theyarn tension temporarily during the insertion process. In the case of aloom according to the present invention this object is achieved byproviding a tension sensor which is switchable between a detectionposition and a passive position in which the tension sensor does nottouch the weft yarn and by an insertion brake according to the presentinvention wherein a braking element of the insertion brake isconstructed as a weft yarn tension sensor or wherein the brake includesa circular counterdisk, a coaxial braking disk and a tension sensoreither in a passage of the braking disk or on the circumference of thecounterdisk.

During an insertion process, the weft yarn tension is detectedtemporarily and only in phases in which the friction applied to the weftyarn as a result of the detection does not have any negative influenceon the insertion process. In the phase or phases of the insertionprocess in which the frictional influence on the weft yarn, whichinevitably results from the detection of yarn tension, would interferewith or endanger the insertion process, the detection of tension isinterrupted. The tension can be detected individually during eachinsertion process at the moment at which information on the tensionbehavior or absolute tension values are needed. The tension detectioncan individually be adapted from one insertion process to the next sothat the insertion processes can gradually be optimized. The methodrealizes the subdivision of an insertion process into critical anduncritical tension detection phases with respect to optimized insertionprocesses in spite of the tapping of the tension information.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the subject matter of the invention are explained on thebasis of the drawing, in which

FIG. 1 shows schematically a loom having a weft yarn feeder associatedtherewith,

FIG. 2 shows a variation of a detail of FIG. 1,

FIG. 3 shows a variation of a detail of FIG. 1,

FIG. 4 shows a diagram representing an insertion process in the loomaccording to FIG. 1,

FIG. 5 shows a diagram concerning an insertion process in a rapier loom,

FIG. 6A, B show two associated fragmentary sections of an insertionbrake with integrated tension sensor,

FIG. 7,8,9 show variations of details of FIG. 6A, 6B, and

FIG. 10 shows a top view of an additional embodiment of an insertionbrake.

DETAILED DESCRIPTION

A loom W according to FIG. 1, e.g. an air-jet loom, comprises a shed 1with a reed 2, air nozzles 3 as well as a main nozzle 4 arranged on theinlet side and used as a transport means for inserting a weft yarn Y inthe shed 1.

Furthermore, a weft yarn feeder 5 belongs to the loom W, said weft yarnfeeder 5 being provided with a stopping device 6 plus associated soppingelement 7 and with a passage sensor 8. Downstream of the yarn feeder 5,a controlled insertion brake 9' is arranged in the weft yarn path, and,downstream of said insertion brake, a controlled tension sensor 10' isarranged in the weft yarn path. A control means 11, which is providedwith a synchronization device 12 in the case of the separate arrangementof insertion brake 9' and tension sensor 10' shown in FIG. 1, isconnected to the individual components of the loom and of the yarnfeeder by a signal-transmitting, signal-receiving or controllingconnection, as has been indicated by the broken lines.

In the course of each insertion process of a weft yarn section, whichhas been dimensioned by means of the stopping device 6 in the yarnfeeder 5 and which is held with the free weft yarn end in the mainnozzle 4 prior to the insertion process, the nozzles 3 and 4 transportthe weft yarn Y up to the end of the shed 1 facing away from the yarnfeeder 5. Subsequently, before the reed 2 beats up, the weft yarn Y iscut downstream of the main nozzle 4 by means of a cutting device whichis not shown. After the beginning of the insertion process, thecontrolled insertion brake 9' as well as the controlled tension sensor10' are switched over by the control means 11 to their inoperative orpassive positions in which the weft yarn Y is inserted without beingdecelerated. Towards the end of the insertion process, when a whippingeffect may be produced due to the mass of the yarn which is forced tostop and due to the transporting force of the nozzles 3, 4, theinsertion brake 9' is switched to the braking position shown in FIG. 1so as to dampen or suppress a disturbing and possibly even detrimentalincrease in tension. The insertion brake 9' is controlled e.g. on thebasis of passage signals of the passage sensor 8, just as the tensionsensor 10', which can, in addition, be synchronized with the insertionbrake 9' via the synchronization device 12 with respect to its movement.The tension sensor 10' detects the tension behavior in the weft yarntemporarily and transmits to the control means 11 absolute, relative ortemporal information on said tension behavior. The control meansprocesses signals which can be derived from the tension behaviordetected. In the separate arrangement shown in FIG. 1, the tensionsensor 10' can also be moved asynchronously into its detection positionfor determining the tension behavior in the weft yarn subsequent to thedeceleration and the end of the insertion process, respectively, andprior to the beginning of the insertion process until the weft yarnstarts to move, and for deriving information from said tension behavior.

It is, however, important that, in the phases of the insertion processin which friction forces would interfere with the insertion process orbe detrimental to the weft yarn, the tension sensor 10' is in itspassive position and does not apply any friction to the weft yarn Y.

In the case of the embodiment according to FIG. 2, the tension sensor 10is structurally integrated in the insertion brake 9 in such a way thatan insertion brake element, which deflects the weft yarn for the purposeof braking and applies friction thereto, is simultaneously constructedas the tension sensor 10 or as part of said tension sensor 10. This hasthe effect that a friction necessary for detecting the tension behaviorwill be applied to the weft yarn only if the controlled insertion brake9 simultaneously occupies a braking position.

In the embodiment of FIG. 3 (for a rapier loom), the weft yarn feeder 5'is provided with an insertion brake 9 constructed as an axial disk brake13. A storage body 14 of the weft yarn feeder 5' has attached thereto acounterdisk 15 at the end face thereof, said counterdisk having acircular circumference. The counterdisk 15 has coaxially associatedtherewith a braking disk 16, which has a central passage 17 and whosedistance from the counterdisk 15 is adapted to be adjusted up to andinto a position of contact with the aid of a controlled drive means 18,e.g. by the control means 11, during an insertion process. The weft yarnY is drawn off the storage body 14, and, in the course of this process,it circulates around the circumferential edge of the counterdisk 15before it is rerouted inwards between the disks 15 and 16 and axiallywithdrawn through the passage 17 provided in the braking disk 16. Due tothe rerouting and clamping, the braking process can be controlledprecisely. If the braking disk 16 is controlled such that it is locatedfar from the counterdisk 15, the then only mild rerouting of the weftyarn will avoid any detrimental frictional influence on the rapier loomduring the insertion process. The tension sensor 10 is directlyintegrated in the insertion brake 9, said tension sensor beingintegrated either in the passage 17 or in the circumferential edge ofthe counter disk 15 (indicated by a broken line).

In the diagram of FIG. 4, the vertical axis represents the weft yarntension and the horizontal axis represents the time. The process shownin said diagram is a single insertion process. Curve A, which consistsof solid lines, represents the tension behavior in the weft yarn duringthe insertion process when the controlled insertion brake 9', 9 is used.Curve component B, which consists of broken lines, represents thetension behavior in cases in which the weft yarn is not subjected to anybraking. The process shown is a typical insertion process in a jet loomhaving a modern structural design. The two time periods H represent thephases of an insertion process during which the tension behavior in theweft yarn is detected. Time period G, however, represents the phaseduring which the weft yarn is accelerated until it has reached itsmaximum speed and is then transported through the shed at said maximumspeed. During the time period G, the tension behavior is not detected soas to avoid the application of any disturbing frictional force to theweft yarn (curve component C, shown by a dot-and-dash line astheoretical tension behavior). ta is the moment at which the insertionbrake becomes effective. a is the period of time during which braking iscarried out. tB represents the end of the braking process and,simultaneously, the occurrence of an extreme tension peak which wouldoccur in the tension behavior at the end of the insertion process if nobraking were effected (curve component B consisting of a broken line).tB also represents the moment at which a second increase in tension eoccurs; due to the braking force applied, said second increase intension e is, however, much lower than the extreme increase in tension Boccurring if the weft yarn is not decelerated. d is a first increase intension caused by the braking operation. h is the tension behaviorbefore the insertion process starts in a condition in which the weftyarn is standing still. h is followed by a tension drop b representingat E the start of movement and, consequently, the release of the weftyarn in the stopping device 6 of the yarn feeder 5. In the curvecomponent f, the tension behavior gradually changes towards h because ofthe weft yarn which has come to a standstill. K represents a tensiondrop when the weft yarn is cut. Curve component g represents at D anincrease in tension upon beating up of the reed, said curve component gbeing followed by curve component h.

Below the horizontal axis t, a parallel time axis t is shown, which hasapplied thereto the passage signals (e.g. 1 to 10 for ten turns whichhave been drawn off) occurring during the insertion process. For thepurpose of setting the control means 11, insertion is, for example,first carried out without any braking being effected for determiningthus the moment tB which occurs in the case of one type of yarn duringeach insertion process in a fixed temporal relationship and at the endof the insertion process, said moment tB representing the end of theinsertion process. In the case of each insertion process, the same timeinterval X elapses between tB and a passage signal which has to bechosen, e.g. the passage signal No. 5. By subtracting from the timeinterval X the braking period a, which has been determined to beexpedient for this type of yarn, the time interval x1 is ascertained,said time interval x1 being the time which has to elapse after theoccurrence of passage signal No. 5 before the insertion brake 9', 9 isactivated. The response time of the insertion brake is, of course, takeninto account in this connection. The tension behavior detected (curve A)can be used for deriving therefrom information for the control means 11so as to be able to find out at which moments and to which extent andfor which periods of time the above-mentioned characteristic tensionvariations occur. This permits a determination of correction signals foradapring the control of e.g. the insertion brake 9', 9, the nozzles 3,4, the cutting device (not shown), the stopping device 6 and the like,said correction signals being then taken into account for futureinsertion processes or being registered as positive acknowledgements oras failure reports. The measure of detecting the tension behavior offersthe possibility of controlling the insertion brake 9', 9 in the bestpossible manner, i.e. the undesirable excessive increase in tension atthe end of the insertion process will be reduced effectively and,notwithstanding this, it will be guaranteed that insertion conditionsexist which have been optimized to a very large extent within the periodof time required for an insertion process and predetermined by the typeof loom used, that the weft yarn does not break, that it lies in theshed in a stretched condition and that the freee weft yarn end hasproperly reached the end of the shed. In principle, it would suffice todetect the weft yarn tension essentially during the time period a. Theadditional information on changes in the tension behavior prior to thebeginning and after the end of the insertion process are, however, alsoimportant so that tension detection can also be extended to these timeperiods during which the frictional load applied to the weft yarn in thecourse of the tension detection does not exert any disturbing influence.The interruption of the tension detection caused by the control of thetension sensor 10' and 10, respectively, during the time period G will,however, avoid a disturbing influence on the insertion process and adetrimental influence on the weft yarn.

The diagram according to FIG. 5 shows a typical insertion process for arapier loom on the basis of the tension behavior during the insertionperiod or during the 360° range of rotation of the loom. Curvecomponents A, which consist of a solid line, represent the tensionbehavior when a controlled insertion brake is used, the tension behaviorbeing detected either via a separate and synchronized tension sensor 10'(as in the case of FIG. 1) or by means of a tension sensor 10 integratedin the insertion brake, this possibility being shown e.g. in FIG. 2 and3. Curve components B, which consist of a broken line, represent thetension behavior occurring during conventional methods in the case ofwhich braking is continuously effected throughout the insertion process.Curve components C, which consist of a dot-and-dash line, represent thereduced increases in tension due to the insertion brake which iscontrolled such that it occupies its position of rest, this being alsothe phases during which no tension detection is carried out. It can beseen that, in curve components C, the increases in tension are muchlower than those in curve components B where braking is continuouslyeffected, whereas in the central area J of curve A the tension dropoccurring during controlled braking corresponds to that occurring duringpermanent braking. Braking is effected during the time periods H(respective braking periods a1, a2, a3), whereas, in the intervalsbetween said time periods H, the insertion brake is controlled such thatit occupies its position of rest. The tension in the weft yarn is onlydetected during the time periods H. In the case of a rapier loom,braking is effected because the first gripper will reliably take up theweft yarn end only if a certain retaining force is effective in the weftyarn, because the first gripper will reliably transmit the weft yarn endto the second gripper only if the weft yarn has applied thereto aretaining force, and, finally, because the second gripper will releasethe weft yarn end reliably and fully stretch the weft yarn if aretaining force is also effective at the end of the insertion process.In the intermediate acceleration and deceleration phases, braking of theweft yarn is, however, disadvantageous. As far as the control andsupervision of the insertion processes is concerned, the information isimportant, which, on the basis of the tension behavior detection, showse.g. that the weft yarn started its motion at the tension peak E, thatthe weft yarn is properly cut when the tension drop K occurs, and that,when the increase in tension D occurs, the correct time interval betweenbeating up of the reed and the other tension variations is confirmed.

In a rapier loom, the control of weft yarn deceleration and of weft yarntension detection according to the diagram of FIG. 5 can be achieved ina particularly advantageous manner by means of the axial axial diskbrake 13 according to FIG. 3 whose drawing-off resistance in theposition of rest is so small that it will not influence the insertionprocess of the rapier loom; it is, however, possible to control saiddisk brake 13 precisely and sensitively enough for applying the brakingforce precisely at the important times during the insertion process andfor performing then also the yarn tension detection.

The insertion brake 9 according to FIG. 6A, 6B, which is particularlyuseful as an insertion brake for jet looms, especially air-jet looms,because, when in its position of rest, said insertion brake 9 permitsthe weft yarn to pass without causing any friction at all, comprises ona stationary basic body 22 an eyelet as a stationary rerouting element19 and two additional rerouting points 20 and 21 in the form of pins,said rerouting points 20 and 21 being spaced apart in the direction inwhich the yarn passes. A shaft 23, which is arranged in said basic body22, is acted upon by a reversible driving motor 24, e.g. a steppingmotor or a d.c. motor; with the aid of the control means, said drivingmotor can be controlled such that will change its respective directionof rotation during an insertion process in a fast-responding andprecisely predeterminable manner and that it will move to respectiveprecisely reproducable rotary positions. A lever 25 is connected to theshaft 23 such that it is secured against rotation relative thereto, saidlever 25 carrying two braking elements 26, 27 in the form of pins whichare adapted to be moved across the yarn path by means of said lever. Inthe position of rest shown, the weft yarn Y is not touched. When thelever 25 is moved anti-clockwise in FIG. 6A, the braking elements 26 and27 will pass between the rerouting elements 19, 20 and 21, whereby theweft yarn Y will be rerouted several times, for decelerating the weftyarn. The insertion brake 9 has integrated therein a tension sensor 10,said tension sensor being defined e.g. by the braking element 27 or bythe rerouting element 20. According to FIG. 6B, the tension sensor 10 isprovided with a sensing element 29; said sensing element is, accordingto FIG. 7, 8 and 9, a piezoelectric sensing element 30 on the base ofthe braking element 27 or of the rerouting element 27 or of thererouting element 20, or it is a strain-gauge element 31. Furthermore,it is possible to provide the tension sensor 10 with a capacitivesensing member 32 and to hold--for the purpose of detecting the yarntension of the weft yarn Y abutting on the rerouting element 20--saidrerouting element 20 in the basic body 22 in a resilient support 33 aswell as to provide it with an extension 34 whose distance or movement isdetected by the capacitive sensing member 32. In this connection, itwill be expedient to determine the tension in the weft yarn on the basisof the signal of the respective sensing element 29 and then on the basisof the rerouting angle of the yarn which is adapted to be derived fromthe rotary position of the shaft 23 and of the motor 24, respectively.

The insertion brake 9 according to FIG. 10 is also preferably used for ajet loom, especially an air-jet loom, because in its position of rest(shown by solid lines in FIG. 10) it will permit frictionless andcontactless passage of the weft yarn Y and because only in its brakingposition (one braking position is indicated by broken lines) it willdecelerate the weft yarn Y in a precisely controllable manner byrerouting it at several points. The stationary rerouting elements 19 and21 are provided in the form of eyelets on the basic body 22. Saideyelets have provided between them a coaxial tubular body 37 whichdefines additional stationary rerouting points 35 and 36 with its ends.The movable braking elements 27 and 26 are attached to the two ends ofthe lever 25, which is indicated by a broken line, and they arepositively connected to the drive 24 via the shaft 23. If the shaft 23rotates anti-clockwise in FIG. 10, the movable braking elements 27 and26 will be displaced to the positions which are indicated by a brokenline and in which the weft yarn will be rerouted six times, all told,and at the same time effectively be decelerated. The movable brakingelement 27 can be provided with a sensing element 29 and it can thus beconstructed as a tension sensor 10. It is, however, just as wellimaginable to construct one of the rerouting elements 19 or 21 as atension sensor or--as indicated--to unite the tension sensing element 29with the stationary rerouting element 35 and to construct the tensionsensor 10 at this location. The tension in the weft yarn Y is detectedwhen the insertion brake 9 has been displaced to a braking position. Ifthe insertion brake 9 is, however, in its position of rest, the tensionof the weft yarn Y will not be detected and, consequently, nodetrimental friction will be applied to the weft yarn.

The following functions and supervisions, which can be carried out bythe above-mentioned tension sensor which is adapted to be switched over,are essential to the invention:

due to the fact that the tension behavior is supervised, a precisecontrol of the braking effect will be possible at the end of theinsertion process, and this will avoid weft yarn faults in the wovenfabric and eliminate the undesirable retraction movement of the weftyarn after the whipping effect. The continuous supply of air to thetransport nozzles in the shed can thus be reduced or switched off at theend of the insertion process and this will result in a desirably lowpressure of the transport nozzles and in a reduced consumption of air.In view of the fact that the time required for stabilizing the weft yarnat the end of the insertion process is now much shorter, the wholeperiod of time available for the insertion can be utilized much betterfor a more effective insertion process.

The precise information which makes known the end of the insertionprocess and which can be derived from the tension behavior permits anadjustment of the time delay between the last reliable passage signaland the moment at which the insertion brake is activated. Furthermore,it is possible to exactly determine, through the tension behavior, theresponse time of the insertion brake under different conditions.Attempts to develop a frictionless tension sensor have already been madefor a long time. The tension sensor of the type explained in the presentconnection, which can be switched over, acts as a frictionless tensionsensor at least in the phases of the insertion process in which thefriction would interfere with the insertion process.

The measure of detecting the tension in the period before the beginningof the insertion process until the weft yarn starts its motion providesuseful information which will show whether or not the main nozzle hasproperly started to work. If the tension behavior detected showsatypical irregularities, the adjustment of the main nozzle canadequately be modified on the basis of this information

From an excessive increase in tension at the end of the insertionprocess it can be concluded that the main nozzle did not switch offproperly; an adequate correction can be carried out at any time takinginto account the information on the tension behavior.

The control of the brake and, consequently, of the tension sensor can becarried out by utilization of a trig signal of the loom, or from theyarn feeder, or by a socalled channel-dependent control means.

It is easily possible to detect also absolute tension values by means ofthe tension sensor and to control the brake with respect to specific,absolute, inadmissible tension values. If, however, only relativetension variations are indicated, the control can be carried out on thebasis of a preselected reduction of the tension increase in percent.

More particularly, in the aforesaid loom it is possible to switch overthe tension sensor so that the tension detection can be carried out onlytemporarily and only in phases in which this will not have any negativeinfluence on the weft yarn. The tension sensor offers the possibility ofobtaining, in a phase of the insertion process which is uncritical withrespect to a frictional influence on the weft yarn, information whichconcerns the insertion process and which may possibly be used for thecontrol of subsequent insertion processes.

In the case of the above-described method, a braking frictionalinfluence on the weft yarn is a prerequisite for tension detection, saidbraking frictional influence taking place simultaneously with thetension detection. The reaction forces occurring as a result of theintentional braking are simultaneously used for tension detection in anadvantageous manner.

Further, in the case of the method, the temporary tension detection isextended to the phases prior to and subsequent to the actual insertionprocess; during these phases, no braking is effected. In phases of theinsertion process which are critical with respect to a frictionalinfluence exerted on the weft yarn, the tension detection isinterrupted. By means of the tension detection, information is obtained,which makes known at which moment and with which influence on thetension in the weft yarn the reed, for example, beats up, the weft yarnis cut, the weft yarn is released for insertion and starts to move, orwhether there is perhaps a malfunction. Such malfunctions can bedetected on the basis of deviations from a tension behavior which isforeseeable at least in principle, and they may possibly be correctedfor future insertion processes or used for switching off.

Furthermore, in the case of the above-described embodiment, tensiondetection is started at the moment at which also a braking operation isinitiated. This is expedient in cases in which the tension sensor isseparate from the insertion brake or works separately therefrom.

A structurally simple and particularly important embodiment is providedwherein the tension sensor is integrated in the insertion brake. Due tothe fact that the tension sensor is integrated in the insertion brake, aseparate tension sensor can be dispensed with and an additional frictionpoint at the weft yarn is avoided. The friction applied during brakingand/or the resultant reaction forces and/or the degree of yarndeflection are used for tension detection. The control of the tensionsensor is simple because it is effected through the insertion brake.

A particularly expedient embodiment is, in addition, the embodimentwherein the tension sensor is arranged on an element of the insertionbrake because the tension sensor has small structural dimensions and canbe accommodated at a reasonable price. The tension is detected directlyand at the point at which the reaction force of the weft yarn becomeseffective.

In addition, for the first time, an optimum control in the case ofdouble weft insertion processes is permitted because each controlledtension sensor shows precisely that the end of its weft yarn has reachedthe other end of the shed. With the aid of optical means, this has notbeen possible up to now.

Still further, the tension variations in the weft yarn detected by meansof the tension sensor permit a detection of the actual movement of e.g.the weft yarn end in the shed and an adaptation of the control of theinsertion brake to the actual sequence of movements. Specific tensionvariations occur at comparatively identical positions of the weft yarnin the shed, independently of the speed at which the insertion processtakes place. The passage signals are only approximately representativeof the sequence of movements because mutilating influences, e.g. atake-off balloon, occur between the yarn feeder and the movement of theyarn end in the shed. Although the activation and deactivation of theinsertion brake is carried out on the basis of the passage signals, itis possible to adapt, at least to a large extent, said activation anddeactivation to the actual sequence of movements by means of theinformation ascertained on the basis of the tension behavior. Theinformation obtained by means of the tension detection can also be usedfor adapting auxiliary functions in the course of the insertion processto the actual sequence of movements, e.g. the actuation of transportnozzles, of a cutting means and the like.

In the embodiment where the weft yarn insertion brake is provided with abraking element which is adapted to be moved by means of a controllabledrive from one side of the weft yarn to the other side thereof, saidbraking element coming into contact with said weft yarn in the course ofthis movement and deflecting the weft yarn thus from its stretchedcondition, the braking element is constructed as a weft yarn tensionsensor.

It follows that, in accordance with an independent inventive concept, aweft yarn insertion brake of this type will be particularly useful forthe above-mentioned tasks if the braking element is constructed as aweft yarn tension sensor. A separate weft yarn tension sensor can thusbe dispensed with, and, furthermore, an additional friction point at theweft yarn is avoided. Moreover, this is an easy way of obtaining anarrangement in the case of which the tension will only be detected ifbraking is effected at the same time. In a controlled insertion brake,this will simplify the control of the tension sensor because saidtension sensor will reliably be activated in the phases in which brakingis effected and will reliably be deactivated in the phases in which nobraking is effected.

Also the following embodiment is structurally simple and advantageous.In said embodiment, either the braking element or the rerouting elementis constructed as the weft yarn tension sensor. The measure ofconstructing the rerouting element as the weft yarn tension sensorresults in structural simplifications.

With the above-described single-acting or double-acting rerouting brake,e.g. a crocodile brake, a large and effective weft yarn wrapping anglecan be adjusted for the purpose of braking and because the reactionforces required for detecting the tension can be tapped clearly andprecisely. The drive means is thus used for controlling the insertionbrake as well as for switching over the integrated tension sensor.

A reliable tension sensor, which responds rapidly and which has smallstructural dimensions, is provided in the case of the embodiment usingthe piezoelectric sensing element, the electronic strain gauge or thecapacitive sensing member. The signals, which then have to be furtherprocessed, are obtained e.g. by means of calculations on the basis ofthe measured signals and the yarn rerouting angle at the tension sensorwhich is simultaneously derived from the control, i.e. the tension inthe yarn is determined on the basis of the sensor signals and the yarnrerouting angle at the tension sensor.

Further, with the electric evaluation circuit, the insertion brake iseasy to control because the control means has already supplied theretothe evaluated signals of the detected tension behavior and because saidcontrol means receives, e.g. for subsequent insertion processes,information for a possible adaptation of the control program for theinsertion brake.

In the case of the embodiment of the rapier loom where the insertionbrake comprises a stationary counterdisk having a circular circumferenceand a coaxial braking disk which extends approximately parallel to saidcounterdisk and which has a central passage for the weft yarn, said weftyarn being fed along a circulatory path around the circumference of thecounterdisk, entering then the space between the disk and leaving theinsertion brake through said passage, the axial disk brake isconstructed as a controllable insertion brake in which the tensionsensor is already included, said tension sensor applying, however,friction to the weft yarn only in the activated condition of theinsertion brake, whereas it does not exert any frictional influencewhich would be worth mentioning in phases of the insertion process inwhich the insertion process may be disturbed or in which damage may becaused to the weft yarn.

The above-mentioned aim is achieved in a simple manner by the insertionbrake, which is adapted to be controlled and which, consequently,switches over the tension sensor automatically in such a way that thetension will only be detected in phases in which a braking effect isrequired as well.

The tension sensor according to the present invention can preferablyalso be used for detecting the following conditions and for using themfor the purpose of processing upon controlling the insertion processes:

detection of the noise during tension detection as a confirmation forthe active presence of the weft yarn in the main nozzle;

detection of the tension peaks in temporal respect as a temporalinformation with regard to the fact that an insertion process has beenstarted and finished;

detection of relative yarn tensions,

detection of absolute yarn tension values, e.g. by means of thepiezoelectric, strain-gauge or induction elements; in so doing, theextent to which the yarn is deflected at the moment in question shouldbe taken into account, said extent of yarn deflection being known fromthe position of the control shaft; and

if double weft yarn insertion is carried out, each channel of the mainnozzle should have provided therein a tension sensor as a detector forthe end of the respective insertion process.

That which is claimed is:
 1. A method of controlling the insertionprocess of a weft yarn into a shed of a loom having a reed which isadapted to be moved for a beating up, said method comprising the stepsof accelerating the weft yarn during the insertion process from acondition of standstill at one boundary edge of the woven fabric,transporting the weft yarn through the shed and stopping said weft yarn,and further comprising the steps of exposing the weft yarn temporarilyto a braking friction and mechanically detecting the yarn tension at theweft yarn by a tension sensor, comprising the improvement wherein saidtension sensor is moved from a passive position spaced part from saidweft yarn to a detection position in contact with said yarn for saiddetecting of said yarn tension and wherein the yarn tension is detectedtemporarily during the insertion process.
 2. A method according to claim1, wherein the yarn tension is detected while said braking friction isbeing applied.
 3. A method according to claim 2, wherein the yarntension, in addition to said detection during said insertion process, isadditionally temporarily detected during the period in which the weftyarn starts to move at the beginning of the insertion process and/orduring the period at the end of the insertion process during saidbeating up of the reed.
 4. In a loom for woven fabric comprising a shedand at least one weft yarn feeder arranged on one boundary edge of thewoven fabric for feeding weft yarn, said loom further comprisingtransport means for inserting the weft yarns into the shed, a weft yarninsertion brake which is adapted to be moved between a rest position andat least one braking position, and a tension sensor used formechanically detecting the weft yarn tension, said components beingarranged downstream of the weft yarn feeder in the path taken by theweft yarn into the shed and each of said components being connected to acontrol means comprising the improvement wherein the tension sensorincludes displacement means for moving said tension sensor during aninsertion process between a detection position and a passive position inwhich said tension sensor does not touch the weft yarn.
 5. The loomaccording to claim 4, wherein a synchronization device is provided forsynchronizing at least the switching of the tension sensor to thedetection position and the movement of the insertion brake to thebraking position, said synchronization device being provided incommunication with the control means of the insertion brake.
 6. The loomaccording to claim 4, wherein said insertion brake comprises a pluralityof movable braking elements and stationary rerouting elements and thetension sensor is arranged on at least one of said braking elements. 7.In a loom for a woven fabric comprising a shed and at least one weftyarn feeder arranged on one boundary edge of the woven fabric forfeeding weft yarn, said loom further comprising transport means forinserting the weft yarn into the shed, a weft yarn insertion brake whichis adapted to be moved between a rest position and at least one brakingposition, and a tension sensor used for mechanically detecting the weftyarn tension, said components being arranged downstream of the weft yarnfeeder in the path taken by the weft yarn into the shed and each of saidcomponents being connected to a control means, comprising theimprovement wherein the tension sensor includes switching means forswitching said tension sensor during an insertion process between adetection position and a passive position in which said tension sensordoes not touch the weft yarn and wherein a synchronization device isprovided for synchronizing at least the switching of the tension sensorto the detection position and the movement of the insertion brake to thebraking position, said synchronization device being provided incommunication with the control means of the insertion brake.
 8. In aloom for a woven fabric comprising a shed and at least one weft yarnfeeder arranged on one boundary edge of the woven fabric for feedingweft yarn, said loom further comprising transport means for insertingthe weft yarn into the shed, a weft yarn insertion brake which isadapted to be moved between a rest position and at least one brakingposition, and a tension sensor used for mechanically detecting the weftyarn tension, said components being arranged downstream of the weft yarnfeeder in the path taken by the weft yarn into the shed and each of saidcomponents being connected to a control means, comprising theimprovement wherein the tension sensor includes switching means forswitching said tension sensor during an insertion process between adetection position and a passive position in which said tension sensordoes not touch the weft yarn and wherein the tension sensor isintegrated in the insertion brake and is adapted to be controlled insynchronism therewith.
 9. A loom according to claim 8, wherein thetension sensor is arranged on an element of the insertion brake whichfrictionally influences the weft yarn during the braking operation orwherein the tension sensor is the element itself.
 10. A loom accordingto claim 8, wherein a main nozzle is provided for double weft yarninsertion and wherein said tension sensor, which is adapted to beswitched between said detection position and said passive position andwhich is integrated in said separate insertion brake, is provided as aninsertion end detector for each weft yarn.
 11. A loom according to claim8, wherein the weft yarn is in a stretched condition during insertion ofsaid weft yarn into the shed, the weft yarn insertion brake is providedwith a braking element which is adapted to be moved by means of acontrollable drive from one side of the weft yarn transversely to saidweft yarn, and in the course of this movement said braking element comesinto contact with said weft yarn thus deflecting said weft yarn from itsstretched condition, and wherein the braking element of the controlledyarn brake is constructed as a weft yarn tension sensor.
 12. A loomaccording to claim 10, wherein the insertion brake is constructed as asingle-acting or as a double-acting rerouting brake comprising aplurality of movable braking elements and stationary rerouting elements,said controllable drive for the braking elements and said integratedweft yarn tension sensor.
 13. A loom according to claim 12, wherein thetension sensor is a sensor responding to the load applied to saidbraking or rerouting element when the weft yarn is being deflected andselected from the group consisting of at least one piezoelectric sensingelement, an electronic strain-gauge element, or a capacitive sensingmember.
 14. A loom according to claim 13, wherein the tension sensor isconnected via an electric evaluation circuit to the control means forthe drive of the insertion brake.
 15. In a loom for a woven fabriccomprising a shed and at least one weft yarn feeder arranged on oneboundary edge of the woven fabric for feeding weft yarn, said loomfurther comprising transport means for inserting the weft yarn into theshed, a weft yarn insertion brake which is adapted to be moved between arest position and at least one braking position, and a tension sensorused for mechanically detecting the weft yarn tension, said componentsbeing arranged downstream of the weft yarn feeder in the path taken bythe weft yarn into the shed and each of said components being connectedto a control means, comprising the improvement wherein the tensionsensor includes switching means for switching said tension sensor duringan insertion process between a detection position and a passive positionin which said tension sensor does not touch the weft yarn and whereinthe weft yarn feeder has provided therein at least one weft yarn passagesensor, which is connected to the control means and with the aid ofwhich successive passage signals are produced during an insertionprocess, and wherein the insertion brake is adapted to be controlled bysaid control means on the basis of said passage signals and on the basisof position signals of the weft yarn in the shed, which are derived fromthe weft yarn tension behavior detected by means of the tension sensor.16. In a loom for a woven fabric comprising a shed and at least one weftyarn feeder arranged on one boundary edge of the woven fabric forfeeding weft yarn, said loom further comprising transport means forinserting the weft yarn into the shed, a weft yarn insertion brake whichis adapted to be moved between a rest position and at least one brakingposition, and a tension sensor used for mechanically detecting the weftyarn tension, said components being arranged downstream of the weft yarnfeeder in the path taken by the weft yarn into the shed and each of saidcomponents being connected to a control means, comprising theimprovement wherein the tension sensor includes switching means forswitching said tension sensor during an insertion process between adetection position and a passive position in which said tension sensordoes not touch the weft yarn and wherein the insertion brake comprises astationary counterdisk having a circular circumference and a coaxialbraking disk extending approximately parallel to said counterdisk andhaving a central passage, said weft yarn being fed along a circulatorypath around the circumference of the counterdisk, entering then thespace between the counterdisk and the braking disk and leaving theinsertion brake through said passage wherein, during an insertionprocess, the braking disk can be controlled such that its distance fromthe counterdisk can be varied up to and into a position of contact withsaid counterdisk by means of a drive connected to the braking disk, andwherein the tension sensor is provided either in the passage of thebraking disk or on the circumference of the counterdisk.